i have a serge and cgs vco at home,but i like the cgs pcb because of its dencity and amounth of components,I did buy plenty of them 18 but i still not build 6 of them finished pcb's onto panels,i wander if its worth it as i have redrawn the PCO and have pcb layout ready and read recently the troubles ppl have with it (not v/oct on 5 oct despite the expensive matched transistor pair,low outputs,and what i can expect more?..)

18 is too many boards to buy if you are not sure about the circuit first. Maybe start with 4?

How do your Serge VCOs compare?

If you want the tracking and output levels of an ASM-1 VCO, I suspect you can fill the board with the resistor values from the ASM-1 schematic.

Probably it can be done by modifying the values of the shaper parts, rather than adding outboard circuitry. Why the saw and pulse are hotter is because it is a saw core VCO, so the saw and pulse don't really need shapers.

I can't work on this now, my bench is packed with projects. But when I can I will look at the circuit and try to see what choices affect the output levels. Also my first oscilloscope should arrive this week, which will make tweaking VCOs a bit easier.

However, I'm more curious what everyone's Saw and Pulse/Sqr outputs are looking like? I'm getting pretty hot signals out of there, seems to be around 8-9Vpp. Is this normal?

yep, the Sq output amplitude is controlled by the 1k and 1k8 resistors. Adjust one of these to make it smaller (or larger). Its a
voltage divider so calc as 1/(1 + 1.8 )*24 = 8.57V p-p
(use 24 for a +/-12V system). The result is approx as few op amp outputs actually swing to the supply voltage, but it is an easy way to calc the resistor values you need.

Built two CGS VCO's simultaneously, the first one was wired up several weeks ago, the second one was wired up yesterday. First one appears to be working just fine (although I haven't been able to calibrate it properly at all...haven't really tried that hard), the second is not. It just seems to be outputting flat voltages of differing value at all of the outputs.

1) Both have identical parts (from the same order for both boards). I've checked that all of the components are the correct values and match the working board.
2) I've inspected for any solder bridges...there are none.
3) I've re-seated and now replaced all of the IC's (with the exception of the 2210, which I do not have any extras of).
4) All pin voltage comparisons between the working board and the non-working board are different. I can't find one reading that's the same...

Oh holy crap. Started checking IC input voltages as suggested, and couldn't find anything with a proper voltage. Went back to the power supply connection and realized that the MOTM style cable I was using had the 0v wire floating on the bus board trace that wasn't actually connected to the power supply.

Pretty much all good now. I still hear a tiny bit of modulation in the Saw and Square outputs when voltage is applied to the VC Shape. This time it's more a timbre modulation than a frequency modulation. Not dramatic, but still there. Is that normal?_________________Esoteric drones and nonlinear distortion
Custom/handmade experimental instruments
macumbista.net

I just discovered the downside to using 10 Ohm resistors instead of links or ferrites. CV applied to the VC Shape affects the Square and Saw outputs as well. Ken helped me work that one out, going back to ferrites now.

How did you work that out?

Why do you think ferrites don't make that problem? They have a resistance, too.

Why do you think ferrites don't make that problem? They have a resistance, too.

Ken helped me with it, changed back on his suggestion.

Actually the way I do ferrites is a wire link through a ferrite bead. Only resistance is that of the wire. I think all ferrites would be the same in that regard.

The plus side of using resistors is that they burn before anything else when you mess up the power connections. I learned that again during the same project _________________Esoteric drones and nonlinear distortion
Custom/handmade experimental instruments
macumbista.net

Are you experiencing the same problem I had with the weird modulations? If it ain't broke, don't fix it! However, since you looked up this thread and the other, I'm guessing maybe you did have some issues..._________________Esoteric drones and nonlinear distortion
Custom/handmade experimental instruments
macumbista.net

Ferrite beads provide EMI Supression/isolation between the module and the power lines... and thus, between modules which can couple noize via the power buss. i use mouser #6623-2743001112LF, $0.13@. macumbista's wire-thru-a-bead solution is a roll-yr-own version of the same thing, glad to know it works but seems complicated to me. a 10r resistor provides less isolation. a straight wire provides none, so it's not a good option.

i'm not clear how those beads isolated signals w/in the module for macumbista--maybe something was coupling across the pos and neg power lines?--but again, glad it works.

sonicwarrior wrote:

I hoped for another solution as I already stuffed some resistors there.

Sounds a bit strange to me (but then I have no real clue of electronics) and Ken should replace the

i'm not clear how those beads isolated signals w/in the module for macumbista--maybe something was coupling across the pos and neg power lines?--but again, glad it works.

I'm no EE, but I'm guessing that the 10R's resistance was interfering with the proper connection of the module to the PSU. Ken suggested "not enough power rail decoupling, too thin power wires, or a PSU that is at its limit" when I described the problem to him, so I started working backwards from there.

I asked if the 10Rs could cause that and he said maybe. I don't think he uses resistors in that position, only ferrite beads. So it's likely he never experienced this problem himself (in fact he wrote he had never heard if it before)._________________Esoteric drones and nonlinear distortion
Custom/handmade experimental instruments
macumbista.net

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